Adolescent obesity is a growing U.S. public health problem. Pregnancy during adolescence may contribute to accumulation of fat due to high levels of gestational gain and metabolic adaptations. In contrast to adult pregnant women, young adolescents continue to gain fat beyond the first half of gestation, have higher gestational gains, and retain more weight postpartum. Recommendations for higher gestational weight gain among adolescents have been based primarily on efforts to promote optimal growth and health of the fetus, but the future health risks to the mother have not been addressed. Although postpartum weight increase is higher among adolescents than adults, the increase relative to non-gravid adolescents of similar maturation stage is not known. Longitudinal studies of adolescents have not examined the effect of pregnancy on growth, body size, and blood lipid profiles since longitudinal data before, during and after pregnancy have not been available. Current knowledge is limited by the following: a) lack of appropriate comparison groups of non-parous adolescents to account for growth and secular trends, b) unavailability of measured weight, height, and metabolic indices before, during and after pregnancy, c) lack of longitudinal measures of dietary intake and physical activity, and d) scarcity of comprehensive data on subjects' race, SES, age at menarche, reproductive history, alcohol use, smoking, hormonal contraceptive use, and other lifestyle characteristics. This study will assess the effects of adolescent reproductive status on: 1) incidence of obesity and 2) changes in growth and health parameters from menarche through adolescence, and will determine whether the effects are comparable for Black and White females. This study will also describe changes in body weight and size among primiparous adolescents according to age at menarche and age at first birth to examine the influence of gestational gain on measures of growth and health, and will determine whether the changes are comparable for Blacks and Whites. This study will combine the existing National Heart Lung and Blood Institute Growth and Health Study (NGHS) longitudinal anthropometric, blood lipid, and health data for a cohort of adolescent females with information that we will abstract from their pregnancy medical records (gestational age and weight gain, maternal and infant health outcomes, and pregnancy complications). We will provide the most accurate estimates to date of the effect of pregnancy on changes in stature, body size and adiposity, and blood lipid profiles relative to non-parous Black and White adolescents controlling for a wide variety of potential confounders. The findings will be examined specifically in relation to gestational gain and provide a scientific basis for pregnancy weight gain recommendations for adolescents.